Not applicable.
Not applicable.
The present invention concerns a method for the production of a quasi-isotropic magnetic alternating field.
An arrangement is described in FR 2 776 864 A1, which permits production of a magnetic rotating field in a room to electrically feed electrical cards as, for example, electronic tickets.
A wireless communication system is known from WO 98/53420, which enables communication between a terminal and a multiple number of portable objects by a modulated magnetic alternating field.
These portable objects are often developed as so-called smart cards. They are also often described as electronic tickets. Such electronic tickets comprise a receiving module and generally include a transmitting module. They generally have a size of 53xc3x9785 mm2. The power supply can occur by a built-in energy source such as a battery and/or by a magnetic alternating field. To minimize the energy consumption, a sleep mode is provided for the operation: at entry of such a smart card into such an alternating field, a voltage is induced by an antenna placed on the smart card, by which the concerned smart card can be set into an active mode. If, following this, no further communication takes place the smart card goes back to the energy-saving sleep mode after a determined time. Such methods and designs of execution of such smart cards are known from EP 0 902 353 and from WO 01/20557 A1. The lower energy consumption resulting from this, allows a higher autonomy. Frequencies of the size 6.78 MHz, 13,56 MHz or 27,1 MHz are common for such applications because of the related near field effects.
Because with the transmitted information, a charge might be connected to a received service, for example a ride with a streetcar or a visit of an exhibition room, a particularly reliable prompting and a reliable transmission are required. Such smart cards are used particularly in means of transport in connection with a transmitting device installed in a vehicle. These transmitting devices are preferably placed in the access area. The smart cards which are carried by persons, show a random orientation, also particularly relative to the magnetic alternating field lines and relative to a transmitting device. The required voltage Ui(t) can thereby not always be induced in the antenna of the smart card. The proportional ratio:             Ui      ⁡              (        t        )              ~          ⅆ              ⅆ        t              ⁢            ∫      A              xe2x80x83              ⁢          B      ⁢              xe2x80x83            ⁢              ⅆ        A            
applies for the voltage.
A stands for the surface of the smart card and B for the magnetic induction, B and dA are vector size factors and linked together by the scalar product.
An object of the present invention is based on indicating a method for the production of a magnetic alternating field, so that a sufficient voltage is induced independent from the location of an antenna placed on a smart card relative to a fixed installed antenna array.
This and other objects are addressed by an antenna array comprising three essentially planar frame antennas with at least a winding each, whereby the defined tiers by the three frame antennas are not plane-parallel each by pairs and that the units of information are supplied sequentially to the frame antennas, whereby a quasi-isotropic magnetic alternating field is radiated from the antenna array; the antenna units are of simple constructive and simple wiring structure, so that these can be multiple arranged without any great effort.
The following advantages may additionally be accrued:
i) A simple installment in the area of access of a vehicle or room results from the simple geometric shape of the antenna array with the supplied periodic signals.
ii) A quasi-isotropic magnetic alternating field can also be produced in a larger area, for example in a railway wagon in a cascaded arrangement of the antenna array, with a respective wiring of a cascade or the geometric positioning of the antenna array.
iii) In a cascade of the antenna arrays with the alternating positioning turned by II, these can be executed identically construction- and circuit-wise, so that a simple installment is guaranteed.
iv) The carrier signal and the units of information to be transmitted can be fed into a spot of the co-axial cable in the cascade of the antenna array with the alternating positioning turned by II.